1. Field of the Invention
The present disclosure relates to a multilayer ceramic capacitor and a method of manufacturing the same, and more particularly to a multilayer ceramic capacitor including a base part and outer electrode layer formed on two sides of the base part, and the outer electrode layer includes first outer electrodes formed with the base part together by a sintering manner, and second outer electrodes formed by solidifying a mixture of metal powder and resin; the process of forming the first outer electrodes of the outer electrode layer is performed at about 1300° C., and the subsequent process of forming the second outer electrode or the plating process for forming further-outer electrodes is performed at about 250° C. or lower temperature, and the material of the second outer electrode is mixture of resin and metal powder to replace the glass material used in prior art, so as to prevent glass thermal diffusion during the process of forming the second outer electrode, or prevent plating solution or other impurity from penetrating into the ceramic dielectric during sequential process of plating metal film, thereby maintaining entire strength, higher capacitance and higher stability of the multilayer ceramic capacitor.
2. Description of the Related Art
In recent years, electronic products and their related electronic devices must use active and passive components. An active component (such as IC or CPU) can perform arithmetic processing function independently; and compared with the active component, the passive component does not change the resistance or impedance thereof during a change in the current or voltage applied on passive component. The common passive components generally include capacitor, resistor and inductor, which are called the three major passive components. In terms of function, the capacitor stores charges in electrostatic manner and can discharge within a predetermined time, and can be used for filtering or side-wave coordination. Resistors can be used to adjust the voltage and current in the circuit. Inductors can mainly be used to filter current noise or prevent electromagnetic interference. At present, all information devices, communication devices, consumer electronic devices or advanced electronic products are designed to achieve the purpose of electronic loop control by using these three passive components in cooperation with each other. Because of the wide application scope of electronic products, the requirement for capacitors among passive components has been raised, for example, the size of the capacitor is required to be smaller, or the capacitor is required to have higher dielectric stability.
According to the material, the capacitors can be classified into aluminum electrolytic capacitors, ceramic capacitors, plastic film capacitors, tantalum capacitors and mica capacitors. Compared with the electrolytic capacitor and the tantalum capacitor, the ceramic capacitor has characteristics of higher dielectric constant, better insulation, better heat resistance, smaller size, better stability, and better reliability, and is suitable for mass production, and is capable of withstanding higher voltage and higher heat, and operating in a wider temperature range. Furthermore, the ceramic capacitor can be implemented as a chip to be directly soldered by surface mount technology so manufacturing speed and quantity of the ceramic capacitor is much higher than that of the electrolytic capacitor, the tantalum capacitor and other capacitors. The ceramic capacitors are various, for example, circular plate ceramic capacitor, disc ceramic capacitor, and multi-layer ceramic capacitor are common typical ceramic capacitors available in market.
The multilayer ceramic capacitor mainly includes barium titanate with high dielectric property, and the capacitance of the multilayer ceramic capacitor is usually proportional to a size of a product surface area and a number of stacked layers of ceramic film of the multilayer ceramic capacitor. Generally, the multilayer ceramic capacitor includes inner electrode layers and ceramic dielectric layers stacked in interval by a staggered manner, so as to form capacitors electrically connected in parallel. In other words, each ceramic dielectric layer is sandwiched by the upper and lower electrode layers to form a flat capacitor, and then electrically connected to an outer electrode layer. Therefore, the multilayer ceramic capacitor can be used as a container for storing electricity. The multilayer ceramic capacitor has a larger number of stacked layers of ceramic dielectric layers and inner electrode layers, so the multilayer ceramic capacitors are the most popular and widely used ceramic capacitors in electronic products such as portable high-end electronic products and communication products, for example, PC, mobile phones, automotive electronics and so on.
Japanese Patent Publication No. 5-3131 discloses a multilayer ceramic capacitor including a multilayer body in which inner electrodes and ceramic dielectrics are alternately stacked, and an outer electrode layer. The inner electrode of the multilayer ceramic capacitor is formed by nickel, and the outer electrode layer on two sides of the ceramic dielectric includes first outer electrodes, second outer electrodes formed by combining glass and silver (or silver alloy) at outside of the two first outer electrodes, and third outer electrodes formed by plating metal film on the two second outer electrodes. Because of high sintering temperature, a diffusion layer of nickel oxide may be formed around the area where the ceramic dielectric and the first outer electrode formed by nickel are adjacent to and bonded with each other, so that the bonding strength can be improved. However, during the process of forming the second outer electrodes, the vitreous material may thermally diffuse into the first outer electrode and the ceramic inductor easily because the vitreous material has a very high sintering temperature and long sintering time, and it may reduce the structural strength of multilayer ceramic capacitor or the dielectric. In addition, since the second outer electrode includes both glass powder and silver (or silver alloy) material, uneven distribution of glass powder may occur. When the glass powder accumulates in the periphery of the second outer electrode or is intensively distributed, the plating solution (for example, nickel) may penetrate into the ceramic dielectric easily through diffusion path of the second and first outer electrodes during the process of plating the third outer electrodes on the second outer electrodes, and it may cause bad compactness and poor quality of the multilayer ceramic capacitor and make the multilayer ceramic capacitor fragile and easy to crack. When applied to electronic product, such multilayer ceramic capacitor cannot provide the expected normal function of the multilayer ceramic capacitor, so the conventional multilayer ceramic capacitor are many problems to be solved.
In the process of manufacturing the conventional multilayer ceramic capacitors, multiple heating or sintering processes are performed to produce the multilayer structure of the outer electrodes, but frequent sintering or overheating processes may damage the capacitor, especially the inner electrode and the first outer electrode. In order to produce a high-capacity multilayer ceramic capacitor and increase the number of the stacked inner electrodes, the inner electrodes are designed to be thinner, and it results in a much smaller contact area between each inner electrode and the first outer electrode. In this case, if the already formed first outer electrode is affected by the temperature of the subsequent process to undergo thermal expansion, the original contact part of the first outer electrode with the inner electrode may be damaged or broken to affect the electrical characteristics of the multilayer ceramic capacitor. Furthermore, the outer electrode or the first outer electrode of the conventional multilayer ceramic capacitor may include copper-containing metal or copper. However, the different types of materials have different thermal expansion coefficients, and when the volumes of the heated outer electrode and the heated inner electrode changes, the contact part of the first outer electrode with the inner electrode may also be easily broken.
As mentioned above, the conventional multilayer ceramic capacitor has the above-mentioned problems, in particular, the uneven distribution of glass causes the problem that the plating solution penetrates into the ceramic dielectric during the process of forming the outer electrode, and it causes stability degradation of the conventional multilayer ceramic capacitor. Therefore, what is needed is to solve the problem that the glass powder material or other impurity element may diffuse and penetrate into the multilayer ceramic capacitor.